1. The Field of the Invention
The present invention is in the field of upgrading heavy hydrocarbon feedstocks such as heavy oil and/or coal (e.g., coal liquefaction) into lower boiling, higher quality materials.
2. Related Technology
World demand for refined fossil fuels is ever-increasing and will eventually outstrip the supply of high quality crude oil. As the shortage of high quality crude oil increases there will be an increasing demand to find ways to better exploit lower quality feedstocks and extract fuel values from them.
Lower quality feedstocks are characterized as including relatively high quantities of hydrocarbons that have a boiling point of 524° C. (975° F.) or higher. They also contain relatively high concentrations of sulfur, nitrogen and/or metals. High boiling fractions typically have a high molecular weight and/or low hydrogen/carbon ratio, an example of which is a class of complex compounds collectively referred to as “asphaltenes”. Asphaltenes are difficult to process and commonly cause fouling of conventional catalysts and hydroprocessing equipment.
Examples of lower quality feedstocks that contain relatively high concentrations of asphaltenes, sulfur, nitrogen and metals include heavy crude and oil sands bitumen, as well as bottom of the barrel and residuum left over from conventional refinery processes (collectively “heavy oil”). The terms “bottom of the barrel” and “residuum”(or “resid”) typically refer to atmospheric tower bottoms, which have a boiling point of at least 343° C. (650° F.), or vacuum tower bottoms, which have an initial boiling point of at least 524° C. (975° F.). The terms “resid pitch” and “vacuum residue” are commonly used to refer to fractions that have an initial boiling point of 524° C. (975° F.) or greater.
Converting heavy oil into useful end products requires extensive processing, including reducing the quantity of heavy oil by converting it to lighter, lower boiling petroleum fractions, increasing the hydrogen-to-carbon ratio, and removing impurities such as metals, sulfur, nitrogen and high carbon forming compounds.
When used with heavy oil, existing commercial catalytic hydrocracking processes become fouled or rapidly undergo catalyst deactivation. The undesirable reactions and fouling involved in hydrocracking heavy oil greatly increases the catalyst and maintenance costs of processing heavy oils, making current catalysts less economical for hydroprocessing heavy oil.
One promising technology for hydroprocessing heavy oils uses a hydrocarbon-soluble molybdenum salt that decomposes in the heavy oil during hydroprocessing to form, in situ, a hydroprocessing catalyst, namely molybdenum sulfide. One such process is disclosed in U.S. Pat. No. 5,578,197 to Cyr et al., which is incorporated herein by reference. Once formed in situ, the molybdenum sulfide catalyst is highly effective at hydrocracking asphaltenes and other complicated hydrocarbons while preventing fouling and coking.
A significant problem with commercializing oil soluble molybdenum catalysts is the cost of the catalyst. Even small improvements in catalyst performance can have a  significant benefit to the economics of the hydrocracking process due to the increase in output and/or the reduced use of the catalyst.
The performance of oil soluble molybdenum catalysts depends significantly on how well the catalyst precursor can be dispersed in the heavy oil and/or other heavy hydrocarbon (e.g., coal) feedstock and the concentration of the metal catalyst in the heavy hydrocarbon being cracked. It would be an improvement in the art to provide methods and systems that result in concentration of the metal catalyst within feed streams containing heavy hydrocarbon components requiring additional hydrocracking, which would minimize the overall quantity of catalyst used and improve the overall efficiency and conversion levels, all while minimizing processing costs. 